Controlling the charging of a rechargeable electrical energy storage device, such as a rechargeable battery, by an electrical energy source for such charging is a requirement which is commonly encountered. However, the implementation of such control typically results in inconvenient control equipment and, in some cases, substantial effort by an operator.
The generally favored technique where the signal from the source is subject to substantial variation is the incorporation of a voltage regulator into the control apparatus to lower the voltage of the signal from the source to the approximate level of the fully charged voltage of the device. Then, as the device is charged, the current from the regulator to the device will decrease as the voltage of the device increases, and will be substantially terminated by the matched voltage levels when the device is fully charged.
Regulators of this type, however, can be quite large, and inconvenient as a result of their size and, in some cases, as a result of the heat they generate in dissipating excess energy from the source.
The above technique is, due to the regulation of the voltage level, essentially a constant voltage technique.
Generally viewed as less desirable, but also at times used, is what is substantially a constant current technique. For example, this technique may be implemented by providing a source with a voltage which is much greater than the fully charged voltage of the storage device. Disadvantages in this technique result from the lack of self-regulation and, for some applications, a need to adjust the current at certain stages in the charging process. Typically, the result is increased reliance on an operator with the attendant disadvantages thereof.
With the constant voltage approach, where the source voltage falls below the storage device voltage, to maintain the self-regulation, a mechanism must be employed to in effect uncouple the source from the device when this occurs. This is typically accomplished through a solenoid switch mechanism or, alternatively, by a back-up prevention diode.
In the last few years, with increased experimentation and usage of solar energy, attempts have been made to implement charging control in the context of the charging of a device, such as a rechargeable battery, by a solar panel. Such implementation typically provides a shunt regulator (in parallel with the solar panel) to provide essentially a constant voltage, and a self-regulating situation in the charging mode. Where large currents are generated by the solar panel, regulating apparatus of this type can be exceedingly large and create large amounts of heat. The avoidance of discharging, through the solar panel, when the panel does not even provide enough voltage for the regulator to reach the level of the storage device, is typically implemented through the connection of a diode between the regulator output and the storage device. However, the sacrifice of solar energy by the voltage drop across the diode in the charging mode is a substantial concern, particularly in light of the marginal commercial viability of the employment of solar energy in many applications.
The present invention eliminates the need for voltage regulation of the output of a solar panel which is used to charge an energy storage device. It, in addition, eliminates the energy sacrifice resulting from the utilization of a diode to prevent back-up. Beyond this, in the more general context of the charging of an energy storage device by an energy source, it provides essentially self-regulating control in what is substantially a constant current type charging situation, not predicated on energy dissipation.
In accordance with the invention, apparatus is provided for controlling the charging of a rechargeable electrical energy storage device for providing a storage device electrical signal, by an electrical energy source foer providing a source electrical signal, which source has a charging output terminal and which device has a charging input terminal. Such apparatus, in accordance with the invention, includes: relay means for electrically coupling the charging output terminal of the source and the charging input terminal of the device; signal-testing means coupled to the relay means for receiving the storage device electrical signal and the source electrical signal and for providing an electrical output signal for permitting and preventing such coupling in response to such signals; relay breaker means coupled to the relay means for providing an electrical breaker signal for breaking such coupling after such coupling for a predetermined period of time; and relay driver means coupled to said relay means for providing an electrical control signal for controlling such coupling in response to the output signal of the signal-testing means and the relay breaker signal.
The relay means may include a switch for directly connecting the charging input terminal of the storage device and the charging output terminal of the source. Also, the controlling of the coupling may include reestablishing the coupling in response to the output signal of the signal-testing means upon the breaking of the coupling, with such breaking occurring during the above permitting by the output signal of the signal-testing means. Further, the apparatus may include additional signal-testing means for receiving the storage device electrical signal and for providing an output signal for terminating the coupling in response to the storage device electrical signal, with such terminating occurring during the above permitting by the output signal of the signal-testing means.
In accordance with other apparatus aspects of the invention, the charging control apparatus may be incorporated into a solar to electrical energy conversion apparatus which includes a solar panel as an electrical energy source, and a rechargeable electrical energy storage device which is charged by the solar panel.
Charging control methods, in accordance with the invention, are directed to the methods of operation of the charging control apparatus, including electronic methods, which can be long-term without human intervention.